Biodiesel (B100) is a mixture of long chain Fatty Acid Methyl Esters (FAME) made from natural fats/oils of either animal or vegetable origin. It is most often blended with diesel fuel refined from petroleum to produce blends of diesel and biodiesel. Blends may include 20% biodiesel (B20), 5% biodiesel (B5), or 1% biodiesel (B1). These blends are then combusted in internal combustion engines to power vehicles, electrical generators and the like. Similar blends may also be used as a heating fuel.
The introduction of biodiesel into the fuel stream has led to an additional need for testing for contaminants, such as free acid, mono & diglycerides, glycerin, leftover catalyst and water. ASTM biodiesel standard D-6751 covers specifications for B100 or the pure FAME mixture produced from the bio feedstock. Tests for the amount of B100 in fuel blends are typically performed in the laboratory and include a laboratory test for biodiesel content in diesel fuel blends based on FTIR analysis (ASTM D-7371).